1. Field of the Invention
This invention relates in general to improvements in an internal combustion engine, and more particularly to improvements in a crankcase ventilation system for blow-by gas.
2. Description of Prior Art
It is well known that combustion gas is blown out from an engine combustion chamber into a crankcase through a clearance between a piston and a cylinder, thereby producing blow-by gas within the crankcase chamber. The blow-by gas causes deterioration of engine lubricating oil within the crankcase, and therefore sufficient ventilation for the crankcase is required.
A variety of systems for ventilating the crankcase have been proposed and put into practical use. An example of such crankcase ventilation systems is schematically shown in FIG. 5 and disclosed, for example, in Japanese Utility Model Publication No. 61-152714. As shown in FIG. 6, a V-type engine 51 is provided with two rocker cover chambers 52 respectively formed on the right and left banks. A fresh air introduction passage 55 and a blow-by gas return passage 56 forming part of the crankcase ventilation system are both connected to each of the rocker cover chambers 52, 52. The fresh air introduction passage 55 and the blow-by gas return passage 56 are respectively in communication with the upstream side and the downstream side of a throttle valve in an air intake passage 53 leading to combustion chambers of the engine. Accordingly, blow-by gas (indicated by solid arrows) blown into the crankcase flows into the both rocker cover chambers 52, 52 through passages formed through the engine. Then, the blow-by gas is sucked through the blow-by gas return passages 56 into the air intake passage downstream of the throttle valve 54. Broken arrows in FIG. 6 indicate fresh air.
However, difficulties have been encountered in such a crankcase ventilation system, in which ventilation for the crankcase 57 is insufficient. In other words, since the fresh air introduction passage 55 and the blow-by gas return passage 56 are both connected to each rocker cover chamber 52, a major part of the fresh air flown from the fresh air introduction passage 55 to the rocker cover chamber 52 does not flow into the crankcase 57 and is sucked into the air intake passage through the blow-by gas return passage 56.